These experiments are designed to determine whether adolescents at risk for substance abuse (SA) exhibit impaired cognitive performance on a task that reveals a deficit in performance by adults with a history of SA. Abnormal cognitive performance in adults after long-term exposure to drugs of abuse can reflect either vulnerability to SA (primary effect) or drug effects on the brain (secondary effect). This study tests the hypothesis that a predisposing cognitive deficit in adolescents contributes to risk for substance abuse. To date, 81 adolescents completed the initial phase of the study and 31 have completed their 3-year follow-up visit. Healthy adolescents (N=31) performed similarly to healthy adults on a gambling task (GT), which targets impulsivity and judgment and depends on orbitofrontal cortical function. Substance abusing adults tend to perform more poorly than healthy adults on this task. Adolescents at risk for substance abuse (N=33) also perform more poorly on this task than healthy adolescents, suggesting that abnormal performance on this task may precede exposure to substances of abuse. These results are preliminary and await confirmation by studying a larger population, and assessing directly the significance of the findings in follow-up data. Self-reports and parental reports of difficulties associated with executive function (e.g., planning, organization and initiation) are significantly correlated with an external locus of control in 37 adolescent boys (aged 12-18, with and without ADHD) enrolled in this study. An external locus of control, which has been associated with adaptation and emotional difficulties such as depression and anxiety, is also sensitive to the onset of substance abuse. Follow-up studies of these participants will test the association of perceived control with dysfunctional adaptations such as substance abuse. Using data acquired from adolescents enrolled in this study, we evaluated the inter-rater reliability, internal consistency and/or temporal reliability of a number of the test instruments. We assessed the internal consistency and temporal stability of Conners? Continuous Performance Test (CCPT) as a clinical tool for the assessment of attention-deficit/hyperactivity disorder (ADHD) the CCPT in a sample of 51 adolescents, (19 with ADHD, 8 with ADHD and another disorder, and 24 controls). The CCPT has adequate split-half reliability, and performance was found to be moderately correlated over the span of 1.3 years. ADHD participants tended to perform worse than controls during the first, but not second, CCPT administration. The CCPT was found to be an insensitive indicator of diagnostic status and, while several CCPT performance measures correlated with parent ratings of ADHD symptomatology, the pattern of these correlations was largely independent of the interpretive guidelines provided in the test manual. We conclude that the poor diagnostic validity and the unclear functional relevance of CCPT scores might confound clinical interpretation of the CCPT. We assessed the inter-rater agreement and internal consistency of the Rey Complex Figure Test (RCFT) in a sample of adolescents enrolled in this study. We found each of the RCFT outcome measures to be associated with clinically acceptable inter-rater reliability estimates. Additionally, we found the copy and recall accuracy scores to be associated with clinically acceptable internal consistency. The organizational scoring method we evaluated, while associated with internal consistency that is acceptable for research purposes, was found to be somewhat below estimates associated with clinical acceptability. We assessed the short- and long-term stability of the Stroop Color and Word Test, a commercially-available version of Stroop?s original task in 87 adolescents. Participants were tested an average of one month apart at baseline and twice more at approximately 15 month intervals. We ffound that all of the commonly used performance indices are associated with practice effects and that the three primary scores, but not the formula-derived interference score, were associated with acceptable reliability.